1. Field of the Invention
The present invention relates to a plasma processing system having a plasma generating mechanism and to a plasma processing method, and more particularly to a plasma working system to be used as a semiconductor device manufacture system suitable for finely working semiconductor elements, an LCD manufacture system and the like, and to a plasma working method.
2. Description of the Related Art
Working semiconductor elements is becoming finer year after year, and the requirements of working size precision are becoming more severe. In a plasma processing system for physically and chemically working a semiconductor wafer by dissolving processing gas by plasma, reaction byproducts generated in the system are likely to be deposited and left on the inner wall of a plasma chamber, so that the wafer processing conditions are substantially changed in many cases. After a number of wafers are processed, the worked shapes of semiconductor elements change and reliable manufacture is impossible, irrespective of that the input conditions of the system are fixed.
In order to deal with this problem, deposits on the chamber inner wall are cleaned by plasma, or the temperature of the chamber inner wall is controlled in order to make deposits hard to be attached. These countermeasures are, however, insufficient for maintaining the wafer working conditions constant.
Since the wafer working conditions continue to gradually change, a worker is required to detect a change in the worked shape of a product before the change may pose some manufacture problem, to disassemble the plasma processing system to exchange components, and to wash the system with liquid or ultrasonic waves.
In addition to a deposited film on the chamber inner wall, various factors such as a processing system temperature cause such a change in the wafer working conditions. Conventionally, the processing conditions are maintained constant by detecting a change in the processing conditions of a plasma processing system and cleaning the system in response to the detected change, or by feeding back the detected results to the input of the system.
A means for monitoring a change in plasma processing conditions is disclosed, for example, in JP-A-10-125660. This publication discloses a method of predicting a system performance or diagnosing a plasma state from an equation between the plasma processing characteristics and electrical signals. An approximate equation representative of the relation between three electrical signals and plasma processing characteristic is obtained through multi regression analysis. Another example is disclosed in JP-A-11-87323. This publication discloses a method of monitoring a plasma processing system from a correlation signal of signals detected by a general detector system having a plurality of detectors and mounted on the plasma processing system. As a method of generating the correlation signal, an equation using ratios of six electrical signals is disclosed. Another disclosure is U.S. Pat. No. 5,658,423. This publication discloses a method of monitoring a system from a correlation signal generated from information including light and a number of signals supplied from a mass spectrometer. As a method of generating the correlation signal, main compositions are analyzed.
In the method disclosed in JP-A-10-125660, multi regression analysis is used to obtain the approximate equation representative of the relation between the processing characteristics and the three electrical signals which are obtained from a map formed by changing some input values among a number of processing condition values. Since the number of wafers from which the processing characteristics are measured is too large, it is practically difficult to obtain the equation. Moreover, if the plasma input values not taken into consideration change, the used model equation becomes invalid. If the model equation is required to incorporate the processing characteristics which depend on the internal conditions continuously changing with repetitive wafer processing and being hard to be measured, such as the internal conditions of a deposited film, a large number of experiments for obtaining the processing characteristics are required so that it is very difficult to realize this approach.
The method disclosed in JP-A-11-87323 is a generally used method which uses the correlation signal of a plurality of signals detected with detectors. A disclosed method of generating the correlation signal uses ratios of signals, which applies conventional techniques. A plasma processing system takes various conditions in accordance with many factors of changing the conditions. It is difficult to realize from this disclosure a specific system for correctly monitoring the various conditions of a plasma processing system.
U.S. Pat. No. 5,658,423 discloses a method of monitoring various plasma conditions by checking a change in the system conditions by analyzing main compositions from a large amount of monitored data. A plasma processing system processes wafers having various device structures under various conditions. It is difficult to realize from this disclosure an effective means for performing the disclosed method.